InGaN/GaN multiple quantum well (MQW) structures were grown by MOCVD. A strain-relief underlying layer was employed to reduce the strain in the InGaN well layers arising from the large lattice mismatch between InN and GaN. Samples were investigated by photoluminescence (PL), electroluminescence (EL) and atom force microscopy (AFM) to characterize their optical and morphological properties. By inserting an underlying layer, the PL intensity was increased more than three times. Under small injection current (1-15 mA), the blue-shift of EL peak wavelength was decreased from 8 to 1.8 nm, the surface morphology was improved and the density of V-pits was reduced from 14-16 x 10(8) to 2-4 x 10(8)/cm(2). Further, the 20-mA output power was increased by more than 50%. (c) 2007 Published by Elsevier Ltd.